There are alot a threads that mention preventative ingredients that can be used in your mix. Some have better advantages than others and some are still open for discussion. Try searching for guarantee or preventing re-growth. Both should get you on the right track. You may have to read through a few different threads till you find just what you're looking for, but most of the time you will find more that one good answer. Use your own judgement on what might work best for your situation.
best of luck on getting up and going, you're in the right place to learn all you'll ever need to know.